DC motor harmonics

Discussion in 'General Science' started by amilton542, Oct 31, 2011.

  1. amilton542

    Thread Starter Active Member

    Nov 13, 2010
    Last night I had a dream and it told me there is harmonics in DC motors. I "scribbled" down what I could ready for when I returned home and after an evening of research the results proved negative.

    My question is, are there harmonics in DC motors?

    The assumption would be the AC side of commutation is this correct?
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    Presumably yes on the winding side of the commutator.

    There are most likely current harmonics in a brush-less DCM.

    One also gets radiated electromagnetic noise from the brush arcing in a brushed DCM. Place a small running brushed DC motor next to a radio and tune across the AM band.
    amilton542 likes this.
  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    There are resonances at the speeds where the commutation frequency is matched with
    the winding inductance resonance. It's very obvious (and a problem) in stepper motors.
    amilton542 likes this.
  4. Metalmann

    Active Member

    Dec 8, 2012

    I would say anything that rotates, produces harmonics; some at levels we just can't hear.

    Every machine had it's own personal harmonics. Some motors were in the keys of "G", "C", "A" "Ab", etc. Some motors were easier to hum/whistle/sing along with.;)
    AC and DC, both.
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    In a factory where I was apprenticed in the 80's there was a production line that run at a fixed speed and was real loud, not just sound but the entire air moving at a beat; "chunkata chunkata chunkata" and it just happened to be the exact same tempo as most of the popular radio hit songs in the 80's. Anytime walking through there those particular songs would start going through your brain, which was a little annoying as they were mostly crap pop radio junk songs.

    If that production line ran a bit slower we might have got some classic Led Zeppelin instead. ;)
    Metalmann likes this.
  6. Duane P Wetick

    Senior Member

    Apr 23, 2009
    A useful rule of thumb is to observe the current wave with a scope...if the wave is ragged with lots of steep edges, there are probably lots of odd harmonics (the bad ones) present. This can also be seen in an audible form...when the wave is at full chat (a british expression), the sound is less ragged than at say, half power, when the sound is intense.

    Cheers, DPW, [Everything has limitations...and I hate limitations.]